Door impact beam for an automobile

Abstract

A door impact beam, which is arranged in a door panel structure, comprises a beam body, arranged along the longitudinal direction of a door, and attachment portions arranged individually at two opposite ends of the beam body. The beam body is formed of a heat-treated hollow member steel. The attachment portions are individually fixed to the door panel structure. The beam body has a section in the form of a quadrilateral frame having four sides and four rounded corners. The outer radius of curvature R of each of the four corners is adjusted to a value such that the radius R falls within a range of 1.5 t≦R≦3.5 t, where t is the wall thickness of the hollow member.

What is claimed is: 
     
       1. A door impact beam for use in a door panel structure designed for use in an automobile, the door panel structure having an outer panel and an inner panel, said door impact beam comprising; a beam body including a heat-treated steel hollow member having two opposite end portions;   said beam body being arranged along a longitudinal direction of the automobile;   said beam body having a section thereof in the form of a quadrilateral frame including: four side portions and four rounded corners respectively separating said four side portions, said four side portions and said four rounded corners having a common thickness;   an outer radius of curvature R of each of said four corners being within a range of 1.5 t≦R≦3.5 t, where t is a wall thickness of the hollow member; and     attachment portions positioned respectively at first and second opposite end portions of the beam body, said attachment portions being fixed to a structural portion of the door panel.   
     
     
       2. A door impact beam according to claim 1, wherein each said attachment portion comprises a bracket welded to the beam body. 
     
     
       3. A door impact beam according to claim 2, wherein: said beam body is formed of a hardened steel pipe, and said bracket is formed of a non-hardened high-strength sheet of steel that has a formability characteristic usable for forming automobile structural components.   
     
     
       4. A door impact beam according to claim 1, wherein each of said attachment portions comprises a flat portion formed by cutting open each of said two opposite end portions of the hollow member for a predetermined length and then flatting each thus opened end portion. 
     
     
       5. A door impact beam according to claim 4, wherein said beam body and said flat portions are formed of one steel pipe such that only the beam body is hardened. 
     
     
       6. A door impact beam according to claim 4, wherein each of said flat portions has a plurality of thin-walled portions that are thinner than a wall portion of the hollow member, the thin-walled portion of each of said flat portions being fixed to the door panel structure by at least one spot weld. 
     
     
       7. A door impact beam according to claim 1, wherein the section of said beam body is in the form of a square frame having four sides of equal lengths and four rounded corners. 
     
     
       8. A door impact beam according to claim 1, wherein the section of said beam body is in the form of a rectangular frame having four sides and four rounded corners. 
     
     
       9. A door impact beam according to claim 1, wherein the section of said beam body is in the form of a trapezoidal frame having four sides and four rounded corners.